CVE-2001-0060 in Stunnel
Summary
by MITRE
Format string vulnerability in stunnel 3.8 and earlier allows attackers to execute arbitrary commands via a malformed ident username.
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Analysis
by VulDB Data Team • 05/10/2019
The vulnerability identified as CVE-2001-0060 represents a critical format string flaw within stunnel version 3.8 and earlier implementations. This vulnerability specifically affects the ident protocol handling mechanism within the stunnel application, which is widely used for SSL/TLS encryption services. The flaw exists in how the application processes ident username information, creating an opportunity for malicious actors to exploit the format string vulnerability through carefully crafted malformed input. The stunnel application, designed to provide secure communication channels, becomes compromised when processing ident responses that contain format specifiers, allowing attackers to manipulate memory contents and potentially execute arbitrary code on the target system.
The technical exploitation of this vulnerability occurs when stunnel processes ident username data containing format string specifiers such as %s, %d, or %x without proper input validation or sanitization. When the application attempts to log or process these malformed ident responses, the format string vulnerability allows attackers to control the format string arguments passed to functions like printf or sprintf. This manipulation can result in information disclosure, application crashes, or more severely, arbitrary code execution. The vulnerability operates at the application level where the ident protocol is used for authentication purposes, making it particularly dangerous as it can be exploited during the initial connection establishment phase of secure communications.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on stunnel for secure network communications. The ability to execute arbitrary commands remotely means that attackers could gain complete control over systems running vulnerable stunnel versions, potentially leading to data breaches, system compromise, or further lateral movement within network infrastructures. The vulnerability affects the confidentiality, integrity, and availability of secure communication services, as attackers could disrupt services or extract sensitive information from memory segments. Organizations using stunnel for critical infrastructure protection face potential exposure to sophisticated attacks that exploit this weakness to establish persistent access or conduct data exfiltration operations.
Security practitioners should implement immediate mitigations including updating to stunnel versions 3.9 or later where this vulnerability has been addressed through proper input validation and format string handling. The fix typically involves implementing proper sanitization of ident username data before processing and ensuring that format string functions receive only trusted literal format strings. Organizations should also consider network segmentation and monitoring of ident protocol traffic to detect potential exploitation attempts. This vulnerability aligns with CWE-134 which specifically addresses format string vulnerabilities, and maps to ATT&CK techniques related to command execution and privilege escalation. Regular security assessments and vulnerability scanning should be implemented to identify other potential format string vulnerabilities in legacy applications, as this class of weakness remains prevalent in older software implementations and continues to represent a significant attack surface for cyber adversaries.